From U.S. Pat. No. 4,747,731, an injector-feed device for the pneumatic feed of powder is known, wherein the device conducts fluidized powder from a powder container by means of a horizontal channel arrangement. The horizontal channel arrangement consists of a sensor nozzle, a detector channel which lies axially opposite the nozzle and, downstream from it, a channel outlet which is expanded in cross section relative to the detector channel, a squeeze valve, an injector nozzle disposed axially within a channel segment which has a greater diameter than that of the nozzle, a diffusor channel which is axially opposite the injector nozzle and downstream from it, and a transport channel which follows downstream from the diffusor channel, all arranged serially one after the other. A powder inlet within the powder container extends vertically upwardly into an interstice between the sensor nozzle and the detector channel, so that fluidized powder which rises into the inlet is captured by a carrier gas which flows out of the sensor nozzle and is then transported to the injector nozzle through the detector channel. Propellant gas flows out of the injector nozzle into the diffusor channel arranged downstream from it, and transports the mixture of powder and carrier gas through the transport line to a consumer. Downstream from the diffusor channel, a gas adjustment channel opens into the transport line, by means of which additional carrier gas can be conducted into the powder/air stream. By means of the additional carrier gas, the flow velocity of the powder/air mixture can be changed or adjusted. Because of the horizontal disposition or orientation of the detector channel, powder would settle in it if the powder were not driven through the detector channel by the carrier gas from the sensor nozzle. The amount of gas required to transport a certain amount of powder per unit of time therefore consists of the total amount of the carrier gases from the sensor nozzle and the propellant gas from the injector nozzle. In order to measure the flow amount of the carrier gas, one throttle channel for feeding a small amount of gas opens into the sensor nozzle, and another throttle channel opens into the outlet of the detector channel. The pressures in the throttle channels are measured by means of a differential pressure measurement device. The flow amount of the carrier gas is determined from the differential pressure. Furthermore, a membrane vale is provided which regulates the feed of the propellant gas to the injector nozzle. Rod-like submersible pumps with an injector at the upper end of a pump are known from European patent document EP 0 184 994 B2 and German patent document DE-OS 40 12 190A1. The arrangement of the injector at the bottom end of the pump is known from German patent document DE-OS 41 14 097 A1.
In the pneumatic feed of powder, especially the feed of powdered coating material to a spray nozzle for spray-coating objects, the amount of powder transported per unit of time and the total amount of gas contained in the powder stream are important operational factors. The individual gas or feed amounts, in total, must correspond to the desired total gas amount. The individual gas or air amounts can be measured in a simple manner, for example by means of flow measurement devices, before they mix with the powder. However, a precise measurement of the amount of powder transported per unit of time is a problem.